Why are security experts concerned about "dirty bombs”?
they are easier to build than nuclear weapons.
they are more powerful than nuclear weapons.
they can be sent in letters through the mail.
they specifically target oil supplies.

A

They are easier to build than nuclear weapons.

Explanation:

They are easier to build than nuclear weapons.

Explanation:

Dirty bombs are explosives that spread radioactive material. There's nothing about them that makes them specific for oil supplies. They cannot be send in a letter at all and they are certainly not as powerful as an atomic bomb, which can easily destroy a big city entirely. So we only have left the first option.

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